1. Field of the Invention
The present invention relates to an apparatus for controlling a flow of fine particles, employed for transportation or blowing of fine particles and adaptable to film forming, formation of composite material, doping etc. with fine particles, or a field of fine particle formation.
In the present specification, the fine particles include atoms molecules, ultra-fine particles and general fine particles. The ultra-fine particles mean those generally smaller than 0.5 .mu.m, obtained for example by evaporation in gas, plasma evaporation, chemical vapor reaction, colloidal precipitation in a liquid or pyrolysis of liquid spray. The general fine particles mean fine particles obtained by ordinary methods such as mechanical crushing, crystallization or precipitation. A beam means a flow with a substantially constant cross section along the flow direction independently of the geometry of said cross section.
2. Description of the Related Art
In general, fine particles are dispersed and suspended in a carrier gas and are transported by the flow of said carrier gas.
Conventionally, the control of flow of fine particles in the transportation thereof has merely been achieved by defining the entire flow of the fine particles flowing together with the carrier gas by means of a pipe or a casing, utilizing the pressure difference between the upstream and downstream sides. Consequently the flow of fine particles is inevitably dispersed over the entire pipe or casing defining the flow path, though there is certain distribution in the flow.
In case of blowing the fine particles to a substrate, they are generally ejected with carrier gas from a nozzle. The nozzle employed in such fine particle blowing is a straight or convergent nozzle, and the cross section of the flow of fine particles immediately after the ejection is constricted according to the area of the nozzle outlet. However the flow is at the same time diffused at the nozzle outlet, so that said constriction is only temporary and the flow velocity does not exceed acoustic velocity.
In case of defining the entire flow path of fine particles with a pipe or a casing and of transporting the fine particles with carrier gas along said flow path by means of the pressure difference between the upstream and downstream sides, as gas flow-out at the downstream side for generating said pressure difference not only induces the flow-out of fine particles but also is unable to achieve a very high transport velocity. Also the fine particles inevitably contact the walls of the pipe or casing defining the flow path over the entire course of transportation. Therefore, in case of transporting active fine particles to a desired site, there may result a loss in activity by the time elapsed in said transportation or by contact with the walls of the pipe or casing. Also the defining of the entire flow path of fine particles with a pipe or casing may result, for example by the formation of a dead space in the flow, in a lowered trapping rate of the fine particles and a lowered utilization efficiency of the carrier gas for fine particle transportation.
On the other hand, the conventional straight or convergent nozzle generates a diffused flow in which the fine particles show a broad distribution in density. Therefore, in case of flowing fine particles onto a substrate, it is difficult to achieve uniform blowing and to control the area in which such uniform blowing is obtained.
The U.S. Pat. No. 4,200,264 discloses an apparatus for producing metallic Mg or Ca by carbon reduction method.
In said apparatus, a reduction reaction is caused by heating an oxide of Mg or Ca with carbon in a reaction chamber, and the resulting gaseous mixture is introduced into a divergent nozzle to cause adiabatic expansion for cooling thereby obtaining fine particles of Mg or Ca.
The divergent nozzle employed in said patent is limited to that functioning under an under-expansion condition.
The use of such nozzle under such condition certainly allows to create an supersonic velocity in the passing gas, but the passing gas flow is diffused at the nozzle orifice so that a flow with a substantially constant cross section cannot be obtained.
Consequently there results a low trapping yield in case of trapping the resulting fine particles for example on a substrate